The experimental system developed in our laboratory permits the study of pre-neoplastic cells and events in foreign body tumorigenesis of mice. The pre-neoplastic process is accessible to experimentation during the first few weeks of foreign body reaction, i.e., up to 30 months prior to actual tumor appearance. The insight that may be gained from such investigations is obviously not limited to foreign body tumorigenesis but extends to the general phenomenon of neoplastic cell transformation. Specific areas of investigation include the following: (1) Exact identification and study of pre-neoplastic originator cells which carry the specific information of later tumor characteristics; (2) analysis of factors which determine or influence direction and pace of pre-neoplastic cell "maturation" during year-long latency; (3) study of ultrastructural, subchromosomal, and biochemical-regulatory features in tumor cells with attempts to trace these features back to the pre-neoplastic cell in different stages of "maturation"; (4) search for specific virus or viral genomes; and (5) assessment of the role of immunity in the development of foreign body-induced tumors. BIBLIOGRAPHIC REFERENCES: Brand, K.G. Cell Type of origin and preneoplastic stages in foreign body tumorigenesis. In: "Proceedings of the Second International Conference of Differentiation", Ed. C.N. Muller-Berat, A.S.P. Biol. Med. Press, Amsterdam, 1976. Brand, K.G., Johnson, K.H., and Buoen, L.C. Foreign body tumorigenesis. CRC Critical Reviews in Toxicology, 1977, in press.